Reference link:
Commands examples :
SELECT * FROM USER_OBJECTS;
SELECT * from USER_SEGMENTS;
SELECT * FROM ALL_OBJECTS WHERE OWNER='SCOTT';
SELECT * from DBA_USERS;
SELECT SUM(BYTES) FROM DBA_SEGMENTS ;
SELECT * FROM DBA_TABLESPACES;
SELECT * from DBA_TEMP_DATAFILES;
The data dictionary consists of numerous tables and views created by the database instance. User schemas generally have no privileges on these tables; Oracle Database grants only SELECT access on the views.
Most data dictionary views come in three versions:
Let’s look at an example. Suppose I want to obtain a list of the objects—tables, views, packages, and so on—defined in the database.
The following query returns all the objects defined in my schema:
SELECT * FROM user_objects
This query returns all the objects that are defined in my schema or for which I have been granted the privilege to use those objects in some way:
SELECT * FROM all_objects
Finally, the following query returns a list of all the objects defined in the database instance—if I have the authority to select from the view:
SELECT * FROM dba_objects
Usually the only difference between the USER view and the ALL view is that the latter contains one extra column, OWNER, that shows which schema owns the object.
http://www.dbas-oracle.com/2013/05/dba-view-top-10-to-keep-handy.html
Here I list the Dictionary Views that can one oracle dba use most of the
Times. SELECT_CATALOG_ROLE is a special role to users that allow them to look at DBA views:
Data Dictionary
Where values set in the init.ora file can be viewed – all parameters:
V$PARAMETER
Information about all database objects in the database:
DBA_OBJECTS
Information about all tables in the database:
DBA_TABLES
Information about all indexes in the database:
DBA_INDEXES
Information about all views (including dictionary views) in the database:
DBA_VIEWS
Information about all sequences in the database:
DBA_SEQUENCES
Information about all users in the database:
DBA_USERS
Information about all constraints in the database:
DBA_CONSTRAINTS
Information about all table columns that have constraints on them:
DBA_CONS_COLUMNS
Information about all columns that have indexes on them in the database:
DBA_IND_COLUMNS
Information about all columns in all the tables in the database:
DBA_TAB_COLUMNS
Information about all the roles in the database:
DBA_ROLES
Information about all object privileges in the database:
DBA_TAB_PRIVS
Information about all system privileges granted to all users in the database:
DBA_SYS_PRIVS
Displays all PL/SQL source code in the database:
DBA_SOURCE
Information about all triggers in the database:
DBA_TRIGGERS
Information about object privileges granted to roles
ROLE_TAB_PRIVS
Information about system privileges granted to roles
ROLE_SYS_PRIVS
Information about roles granted to roles
ROLE_ROLE_PRIVS
Information about all tablespaces in the database:
DBA_TABLESPACES
Information about all profiles in the database:
DBA_PROFILES
For all parameters?
V$PARAMETER
General information about the database mounted to your instance:
V$DATABASE
Most information about the performance of the database is kept here:
V$SYSSTAT
Most information about the performance for individual user sessions is stored here:
V$SESSION , V$SESSTAT
Information about online redo logs (2)
V$LOG, V$LOGFILE
Information about datafiles
V$DATAFILE
Basic information about control files, and the two columns it has:
V$CONTROLFILE. STATUS / NAME
An object you can query to obtain a listing of all data dictionary objects (4)
CATALOG, CAT, DICTIONARY, DICT.
When the control file was created, Sequence Number, most recent SCN:
V$DATABASE
Information stored in different sections of the control file, Sequence Number:
V$CONTROLFILE_RECORD_SECTION
To see the names and locations of all control files in the db? (2)
V$PARAMETER. V$CONTROLFILE
Tablespace and Datafiles
Temporary Segments:
Name, tablespace location, and owner of temporary segments:
DBA_SEGMENTS
Size of temporary tablespaces, current number of extents allocated to sort
segments, and sort segment high-water mark information. Space usage allocation
for temporary segments:
V$SORT_SEGMENT
Types of sorts that are happening currently on the database
V$SORT_USAGE
To see the username corresponding with the session:
V$SESSION
Information about every datafile in the database associated with a temporary
tablespace:
DBA_TEMP_FILES
Similar to DBA_TEMP_FILES, this performance view gives Information about every
datafile in the database associated with a temporary tablespace:
V$TEMPFILE
Storage Structures
A summary view, contains all types of segments and their storage parameters,
space utilization settings:
DBA_SEGMENTS
Tablespace quotas assigned to users:
DBA_TS_QUOTAS
Segment name, type, owner, total bytes of extent, name of tablespace storing the
extent:
DBA_EXTENTS
The location and amount of free space by tablespace name:
DBA_FREE_SPACE
The location of free space in the tablespace that has been coalesced:
DBA_FREE_SPACE_COALESCED
Information about datafiles for every tablespace
DBA_DATAFILES
Performance view for information for datafiles for every tablespace
V$DATAFILE
To see the total amount of space allocated to a table?
DBA_EXTENTS
Table creation timestamp, information about the object ID:
DBA_OBJECTS
High water mark, all storage settings for a table, and statistics collected as part
of the analyze (for row migration) operation on that table
DBA_TABLES
Information about every column in every table:
DBA_TAB_COLUMNS
To determine how many columns are marked unused for later removal?
DBA_UNUSED_COL_TABS
To find the number of deleted index entries ?
INDEX_STATS
To determine the columns on a table that have been indexed:
DBA_ID_COLUMNS
The dynamic view to show whether the index is being used in a meaningful way?
V$OBJECT_USAGE
To see whether a constraint exists on a particular column?
DBA_CONS_COLUMNS
To see the constraints associated with a particular table:
DBA_CONSTRAINTS
To find the username, ID number, (encrypted) password, default and temporary
tablespace information, user profile of a user, password expiry date:
DBA_USERS
To all objects, which objects belong to which users, how many objects a user has
created?
DBA_OBJECTS
Resource-usage parameters for a particular profile:
DBA_PROFILES
Identifies all resources in the database and their corresponding cost:
RESOURCE_COST
Identifies system resource limits for individual users:
USER_RESOURCE_LIMITS
Shows all system privileges:
DBA_SYS_PRIVS
Show all object privileges:
DBA_TAB_PRIVS
Shows all privileges in this session available to you as the current user:
SESSION_PRIVS
Views for audits currently taking place are created by this script:
cataudit.sql
a list of audit entries generated by the exists option of the audit command:
DBA_AUDIT_EXISTS
A list of audit entries generated for object audits:
DBA_AUDIT_OBJECT
A list of audit entries generated by session connects and disconnects:
DBA_AUDIT_SESSION
A list of audit entries generated by statement options of the audit command:
DBA_AUDIT_STATEMENT
A list of all entries in the AUD$ table collected by the audit command:
DBA_AUDIT_TRAIL
To determine the roles available in the database, the names of all the roles on the
database and if a password is required to use each role:
DBA_ROLES
Names of all users and the roles granted to them:
DBA_ROLE_PRIVS
All the roles and the roles that are granted to them:
ROLE_ROLE_PRIVS
Which system privileges have been granted to a role:
DBA_SYS_PRIVS
All the system privileges granted only to roles:
ROLE_SYS_PRIVS
All the object privileges granted only to roles:
ROLE_TAB_PRIVS
All the roles available in the current session:
SESSION_ROLES
Which object privilege has been granted to a role:
DBA_TAB_PRIVS
To display the value of the NLS_CHARACTERSET parameter:
NLS_DATABASE_PARAMETERS